1. Field of the Invention
The present invention relates to a fluorescent-substance light emitting element which is provided with a porous-substance layer having a gas phase/solid phase mixed structure, more particularly, a fluorescent-substance light emitting element which is provided with a porous-substance layer having a porous structure formed by microparticles of an insulating material and to a method of fabrication thereof, and to an image rendering device making utilization of such a fluorescent-substance light emitting element.
2. Description of the Related Art
The CRT (Cathode Ray Tube) has been the typical element (device) for causing a fluorescent substance to emit light by making use of a phenomenon of electron emission from a solid substance. However, thin-type field emission displays (FEDs) employing, as an emitter, a cold cathode type micro-electron emitting element have attracted attention in recent years. Such a cold cathode type emitter draws electrons from the surface of a solid substance into vacuum by a tunnel effect or the like with no heating. For example, Spindt type, MIM (Metal-Insulator-Metal) type, BSD (Ballistic electron Surface-emitting Display) type, and other type have been known in the art.
Firstly, Spindt type electron emitting elements are disclosed in U.S. Pat. No. 3,665,241 and other patents. The action of such a Spindt type electron emitting element is that electrons are emitted in vacuum by impressing a high electric field (>1×109 V/m) on the point of a minute conical emitter section composed of a high melting point metallic material such as Silicon (Si), molybdenum (Mo), and the like.
Secondary, MIM type cold cathode emitters have a structure (metal-insulator-metal) formed by sandwiching an extremely thin insulator layer between a pair of metallic electrode layers. Hereby, electrons tunneling through the intermediate insulator layer are emitted into vacuum by impression of a voltage between the metallic electrodes.
Finally, BSD type cold cathode emitters, as set forth in Japanese Patent Kokai Publication No. (1996)250766, have basically the same principle as the MIM type, with the exception that the layer, through which electrons tunnel, is formed of porous polysilicon. Electrons are emitted through such a microcrystal silicon layer, thereby enhancing the energy of excitation of injected electrons. Therefore, the BSD type cold cathode emitter is characterized in that it is superior in the parallelism of emitted electrons.
Of various fluorescent-substance light emitting elements making utilization of the above-described cold cathode emitters, a fluorescent-substance light emitting element employing a Spindt type cold cathode emitter (hereinafter referred to as “the first prior art example”) is shown in FIG. 8. On the other hand, a fluorescent-substance light emitting element making utilization of an MIM (or BSD) type cold cathode emitter (hereinafter referred to as “the second prior art example”) is shown in FIG. 9.
In FIGS. 8 and 9, fluorescent-substance light emitting elements (71, 81) each constitute a single pixel in a screen of an image rendering device. Usually, such a screen is made up of a great number of pixels. Accordingly, FIGS. 8 and 9 typically illustrate configurations of the fluorescent-substance light emitting elements (71, 81) for a single pixel.
Referring to FIG. 8, in the first prior art example, a cold cathode emitter section 72 is formed on an inner surface (upper surface) of a plate-like rear substrate 51 and an anode section 53 comprising an anode electrode 57 and a fluorescent-substance layer 56 is formed on an inner surface (lower surface) of a front substrate 58. The rear substrate 51 and the front substrate 58 are opposed to each other. In addition, a spacer 61 is disposed between the edge of the rear substrate 51 and the edge of the front substrate 58 over the circumference, and the space between the spacer 61 and the edge of the rear substrate 51 and the space between the spacer 61 and the edge of the front substrate 58 are sealed off with paste or the like.
As a result of such configuration, an airtight space 62 is defined between the rear substrate 51 and the front substrate 58, and the airtight space 62 is maintained substantially in a vacuum state. The Spindt type emitter section 72 has a lower electrode 52, an insulator layer 63, a conical structural member 53 formed of Si or Mo, and a gate electrode 54. Furthermore, a voltage (59) is applied between the gate electrode 54 and the anode electrode 57, and a voltage (60) is applied between the lower electrode 52 and the gate electrode 54.
In the first prior art example thus constructed, electrons (hereinafter referred to as “the emitted electrons”) emitted from the conical structural member 53 of the cold cathode emitter section 72 into the airtight space 62 are accelerated by a voltage applied between the gate electrode 54 and the anode electrode 57, and collide with the fluorescent-substance layer 56. As a result, the fluorescent-substance layer 56 emits light.
Further, as shown in FIG. 9, in the second prior art example, an MIM or BSD type emitter section 82 is formed on an inner surface of the rear substrate 51 in place of the Spindt type emitter section 72 of the first prior art example. In the case where the emitter section 82 is of the MIM type, the emitter section 82 is provided with a lower metallic electrode 52, an insulator layer 53, and an upper metallic electrode 54. In the case where the emitter section 82 is of the BSD type, the emitter section 82 is provided with a lower electrode 52, a porous polysilicon layer 53, and an upper electrode 54. And, the voltage (59) is applied between the upper metallic electrode or upper electrode 54 and the anode electrode 57 and, on the other hand, the voltage (60) is applied between the lower metallic electrode or lower electrode 52 and the upper metallic electrode or upper electrode. Other configurations are the same as the first prior art example.
Incidentally, in each of the conventional fluorescent-substance light emitting elements (the first and second prior art examples) making use of a cold cathode emitter, it is arranged such that electrons are emitted into the airtight space 62. Accordingly, it is required that the airtight space 62 is made extremely narrow (approximately about 0.1 mm to about 1 mm) by the use of the spacer 61 in order to maintain stable fluorescent-substance light emitting characteristics. In addition, the airtight space 62 is required to be maintained in a high vacuum state.
Consequently, the prior art fluorescent-substance light emitting elements suffer the following problems.
A first problem is that it is essential to form the airtight space 62 which must be extremely narrow, and it is difficult to prepare the airtight space 62 in a large area with high accuracy.
A second problem is as follows. It is necessary to maintain the interior space of a housing (comprised of the spacer 61, the rear substrate 51, and the front substrate 58) which forms the airtight space 62 in a high vacuum state. Therefore, it is required for the housing to have a structure capable of withstanding pressure. Because of this, it is required that the material of the housing be thickened.
In addition to the foregoing first and second prior art examples, Japanese Patent Kokai Publication No. (2000)285797 and JP Pat. No. 3112456 disclose techniques relevant to the present invention.